package graphBasics.shortestPath;

import java.util.Stack;
import java.util.Vector;

public class Path {
    private Graph G; // 图的引用
    private int s; // 起始点
    private boolean[] visited; // 记录dfs过程中节点是否被访问
    private int[] from;

    // 图的深度优先遍历
    private void dfs(int v) {
        visited[v] = true;
        for(int i : G.adj(v)) {
            if(!visited[i]){
                from[i] = v;
                dfs(i);
            }
        }
    }

    // 构造方法，寻路算法，寻找graph从s点到其他点的路径
    public Path(Graph graph, int s){
        // 算法初始化
        G = graph;
        assert s >= 0 && s < G.V();
        visited = new boolean[G.V()];
        from = new int[G.V()];
        for(int i = 0; i < G.V(); i++) {
            visited[i] = false;
            from[i] = -1;
        }
        this.s = s;
        dfs(s);
    }

    // 查询s到w是否有路径
    public boolean hasPath(int w){
        assert w >= 0 && w < G.V();
        return visited[w];
    }

    // 查询s到w路径，并存放在vec中
    public Vector<Integer> path(int w) {
        assert hasPath(w);

        Stack<Integer> s = new Stack<>();
        // 通过from数组逆向查找从s到w的路径，存放在栈中
        int p = w;
        while(p != -1){
            s.push(p);
            p = from[p];
        }
        // 从栈中依次取出元素，获取元素顺序从s到w的路径
        Vector<Integer> res = new Vector<>();
        while(!s.empty()) {
            res.add(s.pop());
        }
        return res;
    }

    public void showPath(int w) {
        assert hasPath(w);
        Vector<Integer> vec = path(w);
        for(int i= 0; i < vec.size(); i++) {
            System.out.print(vec.elementAt(i));
            if(i == vec.size() - 1) {
                System.out.println();
            }else {
                System.out.print(" -> ");
            }
        }
    }
}
